EXTJS4.2 调用ashx获取菜单数据时，无论怎么也取不到session，请大侠帮忙

EXTJS4.2 调用ashx获取菜单数据时，无论如何也取不到session，请大侠帮忙
using System;
using System.Text;
using System.Data;
using System.Web;
using System.Web.SessionState;
using BLL;

namespace UI.UC
{
    /// <summary>
    /// ExtHandler 的摘要说明
    /// </summary>   
    public class ExtHandler : IHttpHandler, IRequiresSessionState
    {
        MenuBiz menuBiz = new MenuBiz();
        string emptyStr = "[{\"text\":\"空菜单\",\"mid\":\"1\",\"cls\":\"file\",\"leaf\":true,\"expanded\": true,\"children\":[]}]";

        public bool IsReusable
        {
            get
            {
                return false;
            }
        }

        public void ProcessRequest(HttpContext context)
        {            
            context.Response.ContentType = "text/plain";
            context.Response.Cache.SetCacheability(HttpCacheability.NoCache);
           // HttpContext rq = HttpContext.Current;
            //int a = rq.Session.Count;
            if (context.Session["user"] != null) 
            {               
               User user = context.Session["user"] as User;//在这里取不到数据
                string account = user.Account;
                string jsonString = GetWords(account); //这是获取数据库数据组成JSON格式的方法
                context.Response.Write(jsonString);
            }
            else
                context.Response.Write(emptyStr);
            context.Response.End();
        }
}}

web.config


<?xml version="1.0"?>
<configuration>
   <system.webServer>
    <handlers>
      <remove name="ChartImageHandler" />
      <add name="ChartImageHandler" preCondition="integratedMode" verb="GET,HEAD,POST"
       path="ChartImg.axd" type="System.Web.UI.DataVisualization.Charting.ChartHttpHandler, System.Web.DataVisualization, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" />
    </handlers>
  </system.webServer>
  <connectionStrings>
    <add name="Conn" connectionString="Data Source=.;Initial Catalog=xxxx;Persist Security Info=True;User ID=sa;pwd=xxx" providerName="System.Data.SqlClient"/>
     </connectionStrings>
  <appSettings>
       <add key="ChartImageHandler"   value="storage=memory;timeout=20;Url=~/tempImages/;privateImages=false;" />
  </appSettings>
  <system.web>
   
    <httpHandlers>
      <add path="ChartImg.axd" verb="GET,HEAD,POST"  type="System.Web.UI.DataVisualization.Charting.ChartHttpHandler, System.Web.DataVisualization, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35"
       validate="false" />     
    </httpHandlers>
    <pages>
      <controls>
        <add tagPrefix="asp" namespace="System.Web.UI.DataVisualization.Charting"
         assembly="System.Web.DataVisualization, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" />
      </controls>